Various devices are presently used for shutting off power to a motor of an electric hoist when there is an overload applied to the hoist load lift chain or cable, as evidenced for example by commonly assigned U.S. Pat. Nos. 3,075,134 and 3,728,502. More specifically, patent 3,075,134 is illustrative of an overload prevention device which is mounted within the casing of the hoist, and wherein the dead end 93 of the load lift cable is affixed to an overload sensing lever 90 which is pivotally mounted on the hoist casing as indicated at 91 (FIG. 1 of the patent); thereby concentrating all static and any resonant vibrational loads transmitted through the cable 93 to the hoist casing at its points of connections with the pivot pin 91. Also, note that the mechanism of U.S. Pat. No. 3,075,134 operatively requires provision of a relay device such as is illustrated at 41 therein. U.S. Pat. No. 3,728,502 is illustrative of a type of overload protection device which is arranged externally of the hoist casing and therefore is not concerned with the problem which is dealt with by the present invention. However, note that the overload protection device of U.S. Pat. No. 3,728,502 requires provision of a variable spring characteristic type unit as illustrated at 64-60 in the drawing thereof.
The present invention is directed to an improved hoist construction which includes a self-contained overload prevention arrangement, which features a novel overload "snubbing" device in combination with a spring monitored snap action power supply control switch having circuit cutout and reset provisions occurring at different points along the path of travel of the switch actuator; the load "snubber" and the switch monitor mechanism cooperating to distribute static and/or dynamic overloads such as are transmitted through the load lift system to different portions of the hoist frame. Thus, the hoist motor as well as the frame of the hoist and the operative parts thereof are protected from overloads such as may be due either to attempts to statically overload the hoist or to dynamically induced overload conditions.
Other examples of prior art overload protection devices are found in U.S. Pat. No. 2,636,953; 3,095,979 and 3,233,746. However, it will be noted that the prior patents referred to and of which applicant is aware do not provide the improved combination load snubbing and load stress distribution results of the present invention.